Snap action device



Jan. 20, 1959 J, w, WELSH 2,870,292

SNAP ACTION DEVICE Filed June 6, 1957 2 Sheets-Sheet 1 F|G.3 T 12 12 I l ,1! m ll m 15 I as H 15 16 KIo/l 1 13 INVENTOR.

A 2 ATTORNEY Jan. 20, 1959 J. w. WELSH SNAP ACTION DEVICE 2 Sheets-Sheet 2 Filed June 6, 1957 INVENTOR.

5 5 5 w 5 2 1 1 1 1 2 5 1 2\ -.m\ m 1 h E .1 5 1 5 5 Q 5 5 5 Mm 2 2 2 "a 1 21 2, r K M m n Ki /Vivi; v w w 1 w 1 m n A n n A w DE Et LE. Efi it. E I n m n Y. n m m United States Patent O 2,870,292 SNAP ACTION DEVICE James W. Welsh, Summit, N. J., assignor, by mesne assignments, to Hoda Corporation, Great Neck, N. Y., a corporation of New York Application June 6, 1957, Serial No. 663,928

7 Claims. (Cl. 200-113) in my copending application Serial No. 664,034 filed June 6, 1957, for Snap Action Device. The switch or flasher of the present invention may be described as a square wave contact pressure switch in which the contact pressure is increased steadily until the switch snaps to the open position.

In my U. S. Patent No. 2,756,304 of July 24, 1956, I have illustrated and described a novel type of snap action vane, and a switch or flasher incorporating the same, in which a vane of relatively stiff spring metal is given an initial set by providing a pair of aligned and longitudinally spaced deformations extending from diagonally opposite corners of the vane toward the center thereof, the central area of the vane being left undeformed. This gives the vane an initial bend about a first diagonal extending along the deformation.

The vane is pre-stressed to bend about the other diagonal by attaching a thermostatic wire or ribbon to the corners at the ends of the first diagonal, the wire or ribbon being attached in the cold, contracted condition with the vane bent about the second diagonal. When the wire or ribbon is heated and expands, the vane snaps to its initial bent condition about the first diagonal. When the wire or ribbon cools and contracts, the vane snaps back to its condition of being bent about the second diagonal.

It has been found that the manufacture of such snap action vane switches can be greatly simplified and reduced in cost by making the thermostatic operator integral with the vane in a single vane forming operation. This eliminates the time and labor hitherto necessary in pre-stressing the vane and holding it pre-stressed while the pull ribbon or wire is attached to the vane by spot welding or brazing.

In making the vane, a piece of preferably electrically conductive spring metal is used, the metal being selected for high elasticity and resistance to creep under static or dynamic stresses. Other factors important in the selection of the metal are its specific temperature resistance, coefiicient of resistance, and coeflicient of expansion, all of which factors must be considered with particular reference to external or ambient operating conditions.

The metal piece is formed with a closed-end slot extending along and parallel to an edge so as to provide a narrow strip of metal along such edge integral at each end with the much larger body section of the vane. As described in my said copending application, the main body of the vane is then deformed or thinned along a pair of rectilinear zones or lines extending toward each other with a central area of the main body section between the ends of the deformations being left undeformed and free of stress. For example, the deformations may comprise a pair of linear embossments thinning the metal of the main body section along the lines of deformation. This deformation of the main body section results in an initial set being imparted to the vane along a bending line determined by the direction of the deformations. The thermostatic strip is then foreshortened by forming an offset therein at or adjacent its center. This foreshortening of the strip, which latter is integral at each end with the main body section, results in stressing the main body section to bend about a line normal to the strip and at an angle to the initial bending line of the body section.

If the vane is now heated, as by an electric current flowing therethrough, the strip heats and expands much faster than the main body section. The differential expansion of the strip relative to the main body section progressively decreases the stress holding the main body section bent about a line normal to the strip, and the main body section flattens to a point where it snaps to a position bent about its initial bending line as determined by the direction of the deformations therein.

As the vane cools, the differential contracting of the strip again stresses the main body section to bend about the line normal to the strip and, after an equilibrium of forces is reached and just passed, the vane snaps back to its V-shape bent about the line normal to the strip.

The snapping of the main body section between positions bent about a pair of different axes or lines results in there being a substantial amplitude of relative movement between selected points or areas of the main body section and selected points or areas of the strip.

In accordance with the present invention, this relative movement is utilized to provide a snap action switch by fixedly mounting the vane at one of such points on the body section and securing a contact to one of such points on the strip: or alternatively mounting the vane at a point on the strip and securing a contact at a point on the body section. In the stressed condition of the body section (bent about a line normal to the strip) such contact is firmly pressed against a fixed contact, the two contacts being in an electric heating circuit for the vane.

As will be described hereinafter, if the heating circuit is closed, current will flow through the contacts, and through the vane in parallel paths including the strip and the main body section. As the strip expands relativeto the main body section, the flattening of the latter causes contact pressure to increase until the time when the stresses in the vane cause the body section to snap to a position bent about its initial bend line. This causes snap separation of the contacts, diminishing, if not eliminating, deterioration of the contacts due to arcing.

When the contacts separate, the vane heating circuit is opened. As the vane cools, the strip contracts and eventually snaps the body section to bend about a line normal to the strip. The resultant relative movement of the strip and body section re-engages the contacts under their initial pressure. The cycle repeats as long as a control switch in the heating circuit is closed.

For an understanding of the invention principles, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawing.

In the drawings:

Fig. 1 is a plan view of the snap action vane used in the invention switch, as deformed but before securement of a contact thereto;

Fig. 2 is a front elevation view of the vane of Fig. 1;

Fig. 3 is a plan view of the vane with a contact secured to the integral thermostatic vane;

Fig. 4 is a plan view of the vane with a contact secured to the body section;

2, erases Fig. Sisagraphicillustration of theoperation of the; switch during a complete cycle. 7

Referring to Figs. 1 and 2, a vane 10, of suitable thin resilient. metal havinga relatively 'high. electrical resistance, is formed with a slot 11 substantially parallel and adjacent to one side of the vane. Slot 11 divides vane into a relatively narrow thermostatic operating strip and a main body section 12 whose lateral extent. is preferably several times that of strip 15.

As described in my said copending application, body section 12 of vane 10 is deformed aieng a pair of rectilinear lines or zones 13, as by embossing the body section along these lines. Embossments 13 extend to ward-each other but their inner ends are spaced to leave. a central undeformed area 14.

Deformation of body section 12 causes the vane to: have an initial set or bendabout a bending line or axis XX determined by the direction of deformations 13.. However, strip 15 is formed with an offset 16 at its. central area, which foreshortens the strip. This foreshortening constrains body section 12 to bend about a. second line YY which is normal to strip 15 and at an. angle to line X-X. If vane 10 is heated to cause ex-- pansionof strip 15 relative to body section 12, the body section will flatten progressively until the stresses in-- herent due to its initial bend about line XX overbal-- ance the force exerted bystrip 15, at which time body section 12 will snap to a position bent about line XX.

For. convenience hereinafter, the position of the vane:

as bent. about line XX will be termed the initially O bent position, and the position of body section 12 asconstrained to bend about line YY will be termed the stress-deforn ed position. As the vane 10 snaps between these two positions, there is a substantial ampli tudeof relative movement of central area 14- relative to ofiset area 16. In accordance with the present invention, this substantial amplitude of relative movement is utilized to provide a snap action switch by fixedly supporting the vane at one of these two areas and securing an electrical contact to the other area.

Referring to Figs. 3 and 5, in one embodiment of the invention, a contact 17 is electrically and mechanically secured-to offset area 16 of strip 15. The resultant vane 10 is mounted on a conductive metal bracket 2t by welding or brazing central area 14 to a stepped section 21 of the bracket, with an arm 22 of the bracket extending across and in spaced relation to strip 15 and contact 17 on offset area lid. Arm 22 has a sleeve 23 of dielectric material thereon, and a band 24 of conductive metal is wrapped around sleeve 23 and has a contact 25 electrically and mechanically secured thereto. Contact 25 is aligned with contact 17 and engaged therewith under pressure in the stress-deformed position of vane 10.

T 0 provide a heating circuit for vane 1t), bracket is electrically connected to ground through a control switch 26, and strip 24 is connected through a load 27 to the ungrounded terminal of a battery 23 whose other terminal is grounded. When switch 26 is closed current flows from battery 28 through load 27, band 24, contact and contact 17 into strip 15. In strip 15, the current divides and flows in parallel paths to body section 12 and thus into bracket 20 and through switch 26 to ground. When vane 10, after a pre-set time interval, snaps to the initially bent position, as described hereinafter, contacts 17 and 25 are snapped apart to open the heating circuit. The vane then cools until vane 10 snaps back to the illustrated stress-deformed position to snap contacts 17, 25 into engagement. The cycle then repeats as long as switch 26 remains closed.

' Before discussing the theory of operation of vane 10, reference is made to the alternative embodiment of the invention illustrated in Figs. 4 and 6. In this case, a switch vane 10" is formed by electrically andmechanically securing a contact 18 to central area 14 of body section 12. Stepped section 21 of bracket 20 is welded, brazed, or otherwise mechanically and electrically secured Within offset area 16 of strip 15, with section 21 of bracket 20 extending in spaced relation across contact 18. Contact 25, on band 24 wrapped around dielectric sleeve 23 on section 22, is in pressure engagement with contact 25 in the stress-deformed position of vane 10".

The heating circuit is the same as in Fig. 5. When :switch 26 is closed, the vane is heated until it snaps to the initiaiiy bent position with a snap disengagement of contacts 18 and 25, the contact pressure steadily increasing until the moment the contacts snap open. The wane then cools until it snaps back to the illustrated zz-stress-deformed position to re-engage contacts 18 and with a snap action.

Figs. 7 and 8 graphically illustrate the theory of operation of the switch shown in Fig. 5 and incorporating 'vane 10' of Fig. 3. Referring to Fig. 7, when switch 26 is closed, a load current of the value L fiows through the vane until such time as contacts 17 and 25 are snapped apart as vane 10 snaps to the initially bent position. The current then instantly drops to zero until the vane 10' is snapped back to the stress-deformed position with snap re-engagement of contacts 17 and 25. At this instant, the current flow substantially instantaneously re-attains the value L. The time points on intervals indicated by the Roman numerals correspond .to the several positions of vane 10 as diagrammatically .iilustrated in Fig. 8.

In Fig. 8, contact 25 represents a fixed reference point .as it is substantially immovable relative to the vane mounting point on bracket 2%. After switch 26 is closed, the vane It) begins to heat. At time interval 1, the vane is only slightly heated and its length is A-A. The apex angle of the V about stress-deformed axi Y--Y has its smallest value, and strip 15 is under stress to maintain a pressure engagement of contacts 17 and 25. The parameters of this position are largely determined by the mounting of the vane on bracket 2t). It will be noted that the ends of strip 15 are at the level ti--6.

At interval II, further heating of vane 10 has caused strip 15. to expand to length B-B, causing some flattening of body section 12 with an increase in the apex angle at axis Y This tends to raise the ends of strip 15 but, as body section 12 is fixed, relative to contact 25, by virtue of central section being secured to bracket 2%, the strip ends do not move up. The resultant stress is absorbed in an increase in the contact pressure of: contact 1.7 against contact 25.

At time interval III, strip 15 has expanded to length CC with further flattening of section 12 and increase in the apex angle at axis YY. The result is a further increase in the contact pressure due to stresses engendered by flatt ning of section 32.

At time interval IV, the stresses in. section have built up to the point where the vane is ready to snap to the initially bent position about axis Strip l5 lengthened to DD, the apex angle l has increased to near its maximum, the conte pressure has further increased, and the tog le lever stresses between points 14 and 16 has built up nearly to the snap-over point.

inst past interval IV, vane EU 2 .ps to the initially bent position about axis XX. This position is illustrated at interval V where strip 15 has been up to position snapping contacts 17 and apart. Vane 16 has started to cool.

As the vane cools through time intervals V1 and VII, strip 15 contracts to lengths C-C and strip ends remaining at level At inter strip 15 has contracted to length A-A and vane about to snap to the stress-deformed position of in where section 12 'is again bent about a Y-- contacts 17 and 25 snapped into en .gernent under pressure. The cycle repeats as long as switch 26 remains closed.

The arrangement shown in Figs. 4 and 6 may be similarly analyzed. In this case, the zone or area 16 of strip 15 remains at a fixed level with respect to contact 25, and central area 14 of section 12 is moved. The same conditions, of increasing contact pressure until snap opening of contacts 18 and 25, pertain.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. An electric switch comprising, in combination, a snap action vane in the form of a substantially flat piece of a single resilient metal of relatively high electrical resistance having a single relatively elongated closed-end slot extending along and adjacent one edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; said body section having a pair of substantially rectilinear deformations therein extending toward a central area of the body section, the inner ends of the deformations terminating short of each other to leave said central area free of deformation; said deformations determining the direction of an initial bending line about which the vane is bent to a l-shape; said strip having an offset area intermediate its ends foreshortening said strip to bend the body section to a stress-deformed position about a line substantially normal to the strip; vane mounting means fixedly secured to one of said areas; a first contact fixed relative to said mounting means; and a second contact electrically and mechanically secured to the other of said areas, said second contact being pressed against said first contact in said stress-deformed position of said body section; said contacts forming part of an electric heating circuit including said strip and body section whereby, upon energization of said heating circuit, the flow of electric current through said vane will elfect difierential expansion of said strip relative to said body section to elongate said strip to progressively flatten said body section and, after predetermined flattening of said body section, the vane will snap to a position bent about said initial bending line to snap said contacts apart to open the heating circuit; said strip, upon cooling, stressing said body section to eventually snap to said stressdeformed position to snap said contacts together under pressure to reclose said heating circuit.

2. An electric switch comprising, in combination, a snap action vane in the form of a substantially flat piece of a single resilient metal of relatively high electrical resistance having a single relatively elongated closed-end slot extending along and adjacent one edge thereof to divide the vane into a main body section and a strip separated from said body section by said slot and integral with the body section at each end, with the strip having a cross-sectional area only a fraction of that of the body section; said body section having a pair of substantially rectilinear deformations therein extending toward a central area of the body section, the inner ends of the deformations terminating short of each other to leave said central area free of deformation; said deformations determining the direction of an initial bending line about which the vane is bent to a V-shape; said strip having an offset area substantially centrally thereof foreshortening said strip to bend the body section to a stress-deformed position about a line substantially normal to the strip and at an angle to said initial bending line vane mounting means fixedly secured to one of said areas; a first contact fixed relative to said mounting means; and a second contact electrically and mechanically secured to the other of said areas, said second contact being pressed against said first contact in said stress-deformed position of said body section; said contacts forming part of an electric heating circuit including said strip and body section whereby, upon energization of said heating circuit, the flow of electric current through said vane will effect difierential expansion of said strip relative to said body section to elongate said strip to progressively flatten said body section and, after predetermined flattening of said body section, the vane will snap to a position bent about said initial bending line to snap said contacts apart to open the heating circuit; said strip, upon cooling, stressing said body section to eventually snap to said stress-deformed position to snap said contacts together under pressure to reclose said heating circuit.

3. An electric switch as claimed in claim 2 in which said second contact is secured to said offset area of said strip.

4. An electric switch as claimed in claim 2 in which said second contact is secured to said central area of said body section.

5. An electric switch as claimed in claim 2 in which said vane mounting means comprises an electrically conductive bracket electrically and. mechanically secured to said vane and included in said heating circuit; and said first contact is mounted in electrically insulated relation on said bracket.

6. An electric switch as claimed in claim 5 in Which said bracket is secured to said offset area of said strip and extends across said central area of said body section.

7. An electric switch as claimed in claim 5 in which said bracket is secured to said central area of said body section and extends across said offset area of said strip.

References Cited in the file of this patent UNITED STATES PATENTS 2,363,280 Arnold Nov. 21, 1944 2,533,274 Matulaitis et a1 Dec. 12, 1950 2,708,697 Welsh May 12, 1955 2,716,682 Franklin Aug. 30, 1955 2,720,568 Bletz Oct. 11, 1955 

